Active steering systems may continuously and intelligently alter the relationship between a driver's steering inputs at the steering wheel and the angle of the steered road wheels of the vehicle. An active steering system, for example, varies the degree that the road wheels turn in response to rotation of the steering wheel via a mechatronic auxiliary system. At lower speeds, this technology may reduce the amount that the steering wheel must be turned (improving performance in situations such as parking and other urban area traffic maneuvers), and at higher speeds, the system helps to prevent increased steering responsiveness resulting from increased speeds (providing improved direction of stability).
Examples of active steering systems include, but are not limited to, a steer-by-wire system, in which there is no mechanical connection between the steering wheel and the steering of the road wheels, and a superimposed steering system, in which the steering angle that is generated at the steering wheel by the driver is superimposed on a steering angle generated by a servo motor, in a superimposition gear mechanism, and the sum of the two steering angles is transmitted to the steering of the road wheels. Such active steering systems provide various advantages, including, for example, the ability to change the angle of the steered road wheels without the intervention being directly perceptible to the driver. This may be accomplished, for example, by eliminating the coupling of the steering wheel actuation angle and steering angle, in particular to select a transmission ratio between the steering wheel and the steering of the road wheels as a function of the speed, which may increase driving comfort and safety.
Active steering systems may, however, create a situation in which the steering wheel is not necessarily in the center position, and appears to be rotated to the driver of the vehicle, when the motor vehicle is traveling straight ahead. Sources for such visible offsets may include, for example, production deviations, faulty steering wheel settings or steering system settings, and/or wear or damage to the vehicle. Furthermore, uneven roads, with a changing road crown, may also lead to visible offsets between the straight-ahead orientation of the motor vehicle and the center position of the steering wheel. Such deviations may adversely affect the comfort of the driver.
It may, therefore, be advantageous for active steering systems to have knowledge of misalignments between the steering wheel and the road wheels, and be able to correct such steering wheel offsets to make the steering wheel look straight when the vehicle is driving straight.